Pertinent art to the present invention is found in U.S. Pat. No. 4,866,102 and references cited therein. The '102 patent describes a rigid polyurethane foam formed from a polyoxyalkylene polyether polyol having therein a graft polymer dispersion, an alkylene oxide adduct of toluenediamine or methylenedianiline, a crosslinking agent, an organic polyisocyanate, water, catalysts, and an additional blowing agent.